Rust-inhibiting primer composition

ABSTRACT

The novel rust-inhibiting primer compositions are in the form of highly stable emulsions. 
     Besides the per se known components of the film-formers, chelating agents and acid activators, the compositions contain up to 6% W of silica powder, up to 1% W of an anionic heteropolysaccharide and up to 10% W of air-drying oils. 
     In comparison with known agents, the novel primer compositions exhibit improved application properties and enhanced antirust characteristics.

The invention relates to a rust-inhibiting primer which possesses, on account of its novel composition and the method of its preparation, a high storage stability and outstanding application characteristics.

Antirust or rust-conversion agents containing synthetic resins or binders in solution or in emulsion as well as organic chelating agents, in particular tannins, are known. The development of such agents can be clearly followed from the patent literature.

Austrian Pat. No. 149,199, published on 10.04.1937, discloses an antirust agent which contains inter alia tannic acid solutions (tannin solutions) and other organic acids exclusively dissolved, or in solution, in admixture with resins that are soluble in organic solvents, particularly cellulose resins. No reference is made to aqueous emulsions, and the compositions as well as the method of preparation do not appear to be relevant to the invention.

English Pat. No. 826,564, published on 13.01.1960, discloses and claims protecting compositions for metal surfaces which contain acidic vegetable tannin extracts and latexes. Examples 1 and 2 of the said GB patent each describe a mixture consisting of one part by volume of 50% w/v of natural tannins and of the same part by volume of a plasticized polyvinyl acetate latex. Fuller details regarding the composition as well as the problems relating to preparation and storage or use have been omitted. The techno-chemical basis which has led to the English patent referred to, has been published in Journal of Oil and Colour, London, January 1958, pages 10 to 23. The preparation of antirust agents containing tannins and synthetic resin emulsions is represented in the paper more as an objective rather than as a concluded development. This agrees with the examples cited in the English patent which in practice are barely reproducible.

The development then turned more towards the application of solutions containing solely tannins. Examples of such solutions are given in Swiss Pat. No. 513,255, published on 15.11.1975. These rust-stabilizing agents are applied prior to the primer. Finally, Swiss Pat. No. 580,152 discloses and claims compositions comprising chelating agents and hence capable of rust conversion, containing a high proportion of synthetic resin binders.

However, the disclosed agents according to the foregoing Swiss patent leave much to be desired in respect of the storage stability as well as application characteristics and action, in particular as a primer. This is not surprising, given that the chemical problem of mixing an acid solution of a chelating agent with the normally alkaline emulsion of the binder has formerly been a difficult one to solve, for any product which is to be commercially and industrially viable, must possess adequate storage stability and be simple and effective to use. The agent would be most useful if it could find application directly as a primer.

All the mentioned technical improvements have been obtained by the novel compositions according to the present invention; even the applicant's experts could not foresee that the addition of the three key components, viz. silica powder, heteropolysaccharides and vegetable oil, all used on occasions individually in the coatings industry but not known combined in the stated proportions, will bring about such a result.

The rust-inhibiting primer composition according to the invention in the form of a highly stable emulsion is characterized in that it contains, besides solutions and emulsions of film-forming synthetic resins or binders, chelating agents, acid activators and others, up to 6% W--based on total weight--of silica powder, up to 1% W--based on total weight--of an anionic heteropolysaccharide and up to 10% W--based on total weight--of vegetable, air-drying oils and/or phthalate resins modified by such oils and also air-drying; the composition has a minimum water content in respect of storage stability and application characteristics.

The rust-inhibiting primer composition according to the invention can contain as binder both a highly alkaline resistant styrene-butadiene latex, such as finds application for example as cement mortar additive, and a solution of a copolymer based on vinyltoluene and acrylate in white spirit (45% of solids; not more than 17% of aromatic constituents in white spirit); as the vegetable air-drying oil, the composition contains tung oil.

In addition, the novel rust-inhibiting primer composition can contain up to 10% W--based on total weight--of pigments and/or fillers, ground natural quartz being used as filler.

In addition, the composition can contain smaller amounts of emulsifiers, penetrating agents, non-ionic surfactants and organic solvents miscible with water.

The rust-inhibiting primer compositions according to the invention are based on mixtures containing about 10 to 30% W of resins or binders--both based on total weight--as well as such amounts of acid activators that the composition has a pH between 1 and 6.

Examples of resin or binder copolymers are styrene-butadiene, in particular the highly alkali resistant styrene-butadiene latexes, which find use as cement mortar additives, vinyltoluene/acrylate, polyvinyl acetate or polyvinyl alcohol and/or polystyrene butadiene, examples of chelating agents are tannins and/or gallic acid, which may be strengthened in their action by the presence of salicylic acid, benzoic acid, resorcylic acid, resorcinol, hydroquinone and/or pyrogallol, and the acid activators are volatile organic acids.

To prepare the rust-inhibiting primer composition according to the invention, depending on the nature of the components an oily-organic phase is formed and, separately, an aqueous phase; during the emulsification of the two phases silicic acid gel is added.

The novel rust-inhibiting primer composition is used for priming dry iron and steel surfaces by means of various coating methods, a primer coat being thereby produced onto which the usual finishing emulsion coats may be applied.

The term "silica powder" is here understood to mean any amorphous, highly disperse silicon dioxide which is usable according to the invention. Such silicon dioxide products are nowadays generally produced by the flame process.

The term "anionic heteropolysaccharide" is intended to refer to a product obtained in the fermentation of various carbohydrates by bacteria of the genus Xanthomonas (X. campestris). Until a few years ago such products were traded as xanthan rubber.

The term "vegetable air-drying oils or phthalate resins modified with such oils" is understood in this connection to mean above all tung oil, linseed oil, safflower oil, oiticica oil, poppy oil and like vegetable fatty oils; phthalate resins can be modified by these oils relatively easily in a known manner.

The invention will now be illustrated by the examples which follow; the notation used % W refers to percent by weight, based on the total weight of the composition.

EXAMPLE 1

An oily-organic phase is prepared from 30% W of a thermoplastic copolymer based on vinyltoluene/acrylate (45% W dissolved in white spirit), 7.5% W tung oil (stand oil) and a total of 2.5% W of a non-ionic surfactant and plasticizer (paraffin derivative) with slight warming and slow stirring; the said phase is emulsified with 12.5% W of an approximately 50% aqueous, highly alkali resistant latex based on styrene-butadiene.

Separately, an aqueous phase is prepared from 33.5% W of water, 0.05% W of a heteropolysaccharide (Rhodopol 23 ex Rhone-Poulenc S.A.), 7% W of isopropanol, a total of 2% W of a mixture of natural tannin and gallic acid, and 0.55% W of butyl glycol.

While combining the two phases, 4.4% W of silica powder (FK 320 DS ex DEGUSSA) is slowly added under strong stirring with shearing action. A white stable emulsion is obtained which can be readily applied with the aid of a brush, a roller or even a spray gun.

EXAMPLE 2

A rust-inhibiting primer composition with the addition of 8% W of quartz meal (ground quartz stone or quartz sand with a particle size of about 0.1 mm) is obtained when the procedure of Example 1 is followed, except that the amounts added of the components from the first example are reduced by about 2% W for the resin solution, about 2% also for the resin emulsion, about 3% W for water and about 1% W for silica powder. This example yields a viscous white-greyish emulsion which can be easily applied by brush and roller.

Metal components can also be immersed in the above two products and thus primed.

The physiological and ecological advantage of the agent according to the invention lie above all in the absence of heavy metals such as lead, of mineral acids such as hydrochloric acid, and of phosphates. At the same time the composition according to the invention has attained a level of storage stability and application characteristics that is novel for such primers.

The compositions according to the invention are compared with known agents--or those referred to in Swiss Pat. No. 580,152--in the following.

                  TABLE 1                                                          ______________________________________                                         Formulations of the antirust systems to be                                     compared (% by weight)                                                         ______________________________________                                         Formulation 1: based on Kelate ® (1337-V)                                  Kelate ® 51              35%                                               isopropanol                  43%                                               styrene-butadiene            5%                                                water                        17%                                               Formulation 2: based on Swiss Patent 580,152                                   styrene-butadiene-rubber dispersion                                                                         40%                                               butanol                      1%                                                oil dispersion               8%                                                tannin                       2%                                                isopropanol                  6.5%                                              85% formic acid              0.75%                                             water                        40.75%                                            butyl glycol                 1%                                                Formulation 3: based on Swiss Patent 580,152                                   acrylic copolymer            55%                                               polyester resin              3%                                                tannin                       2%                                                85% formic acid              0.5%                                              ethylene glycol              6%                                                water                        43.9%                                             Formulation 4: composition according to the invention                          thermoplastic vinyltoluene/acrylate                                            resin in white spirit        26%                                               drying oil                   6%                                                polyvinylstyrene butadiene   10%                                               heteropolysaccharide         0.07%                                             plasticizer                  1.5%                                              silica powder                1%                                                isopropanol                  6.5%                                              butyl glycol                 2.5%                                              85% formic acid              0.5%                                              tannin                       2%                                                wetting agent                1%                                                quartz (SiO & 2)             12%                                               water                        32.9%                                             Formulation 5: conventional solvent-bound antirust                             formulation                                                                    ______________________________________                                    

    TABLE II       Comparison as regards quality between tannin-containing emulsions based      on Swiss Patent 580,152 and other publications (such as Kelate) with the      technology according to the invention. Quality criteria Formulation I      Formulation 2 Formulation 3 Formulation 4 Formulation 5        appearance dark brown, turbid white emulsion white emulsion white      emulsion red pigmented 1-component      oil/alkyd paint pH 0.6 3.0 3.0      3.0 conversion character- poor film formation, film  strong conversion      after good istics (penetration dries slowly, becomes  first coat      characteristics/film brittle after extended formation) drying period (2      months) application character- strong tendency to run, edge recession,      foaming, edge recession, tendency to in comparison with istics edge      recession tendency to run, sensit- run, weak foaming, very Examples 1      and 2, clearly   ive to slightly greasy sensitive to oils/fats less      sensitive to oils/   surfaces  fats, good edge adhesion     characteristi      cs, good     spraying characteristics,     good adhesion character-      istics on vertical areas,     no foam technical character- istics of the      film Substrate: surface C St 2 C St 2 C St 2 C St 2 C St 2 preparation      of the naturally rusted steel St 37 (1) according to DIN 55928 Applicatio      n method 2 coats 30-50 μm 2 coats 60-80 μm 2 coats 60-80 μm 2      coats circa 90 μm 80 μm (by brush) Adhesion according to embrittlem      ent GT 4 GT 2 GT 2 GT 0 GT 0 DIN 53151 (crosshatch) with additional      strip (compare ASTM-D3359) after a drying period of 3 months Salt spray      test film breaks down after after 100 h after 200 h after 20 hours      according to DIN 50021 100 hours blisters m3/g3 blisters m3/g4 partial      blisters m3/g3 (2) (blisters according  degree of rust R 3 degree of      rust R 3 retrogression after to DIN 53209, degree of  adhesion (5) GT 3      adhesion (5) GT 5 exposure rusting, adhesion (5))    degree of rust R 0         adhesion GT 0 VDA-test (3) accord- film breaks down after after 4      cycles after 4 cycles after 8 cycles after 8 cycles ing to 621-415, re-      4 cycles blisters m4/g3 blisters m3/g3-4 partial blisters m2/g3 blisters      0 inforced with SO.sub.2  degree of rust R 4 degree of rust R 3-4      retrogression, degree of rust R 2-3   adhesion GT 3 adhesion GT 5 degree      of rust R 0 adhesion GT 3     adhesion GT 1-2 Natural weathering film      breaks down com- after 1.5 years after 1 year after 2.5 years after 2.5      years (4) without finishing pletely after 6 months degree of rust R 2      blisters m3/g3 blisters m2/g2 undermigration from the coat  undermigratio      n from the degree of rust R 2-3 degree of rust R 0 side, otherwise film       side adhesion GT 5 adhesion GT 1 intact   adhesion GT 2 undermigration      from the    side Natural weathering after 6 months after 1.5 years  film      chalks, otherwise (4) with acrylic fin- blisters m3/g3 degree of rust R      2 blisters m3/g3 without defect, i.e. ishing coat degree of rust R 3      adhesion GT 3 degree of rust R 2-3 blisters 0  adhesion GT 5  adhesion      GT 5 degree of rust R 0     adhesion GT 1 Physiological aspects strongly      acidic (pH 0.9) unobjectionable unobjectionable unobjectionable (no need      retains solvents strongly,  toxicity class 4 no fire danger no fire      danger to be declared in the fire danger (to be dec-     Swiss toxicity      class), no lared under toxicity class     fire danger 4)      (1) Naturally rusted steel plates:      structural steel St 37, after 6 months naturally weathered in Widnau      pretreatment of steel surface St 2 according to DIN 55928. Rust is remove      to such a degree that after cleaning the steel surface still has a faint      sheen due to metal.      (2) Spray test: temperature in test chamber 35 ±      amount of test solution sprayed onto an area of 80 cm.sup.2 : 1.5 ± 0.      ml per hour      test solution: 5% NaCl solution.      (3) VDA 621415 test:      Cyclic testing of the antirust coating of automotive paints (reinforced      with SO & 2); i.e.: one test cycle: 24 hours, salt spray test according t      DIN 50021      4 days: 4 cycles Kesternich test according to DIN 500018/2.0 l S      2 days: 48 hours at room temperature according to DIN 50014      (4) Natural weathering, i.e. the test panels are without additionally      protected edges in order to follow undermigration: the panels were expose      to the weather at an angle of 45° in a southerly direction      (according to international standards).      (5) Adhesion after exposure: after 1 week's recovery at room temperature      according to DIN 50014, the crosshatch test was carried out according to      DIN 52151.

The comparison tests between known products and an antirust dispersion containing tannins according to the invention indicate, besides improved application characteristics, especially a clearly enhanced rust protection, i.e.:

Improvement with respect to application:

better sprayability

lower tendency to run

excellent edge adhesion characteristics (no edge recession)

no foam formation

Improvement in respect of antirust characteristics:

adhesion after exposure to moisture ano natural ageing

long-term rust protection: active rust protection under atmospheric influence, specifically as regards undermigration

excellent edge protection

antirust characteristics in the corrosion protection tests under alternating cyclic exposure (reinforced with SO₂) 

I claim:
 1. A rust-inhibiting primer composition in the form of a highly stable emulsion comprising:(a) solutions, dispersions and/or emulsions of film forming synthetic resins or binders, (b) chelating agents, (c) acid activators and others, (d) 1-6 wt % based on the total weight, of silica powder, (e) 0.05 to 1% based on the total weight, of an anionic heteropolysaccharide, and (f) 4-10 wt % based on the total weight, of vegetable air-drying oils and/or phthalate resins modified by such oils and also air-drying,the composition having a minimum water content with respect to storage stability and application charactersitics.
 2. Rust-inhibiting primer composition according to patent claim 1, which contains as binder both a highly alkaline resistant styrene-butadiene latex and a solution of a copolymer based on vinyltoluene/acrylate in white spirit, characterized in that the composition contains tung oil as a vegetable, air-drying oil.
 3. Rust-inhibiting primer composition according to patent claim 2, characterized in that the total water content of the composition lies below 50, preferably below 45% W--based on total weight.
 4. Rust-inhibiting primer composition according to patent claim 3, characterized in that it contains additionally up to 10% W--based on total weight--of pigments and/or fillers.
 5. Rust-inhibiting primer composition according to patent claim 4, characterized in that ground natural quartz is used as filler.
 6. Rust-inhibiting primer composition according to patent claim 3, characterized in that it contains in addition smaller amounts of emulsifiers, penetrating agents, non-ionic surfactants and organic solvents miscible with water.
 7. Rust-inhibiting primer composition according to patent claim 1, characterized in that the content of resins or binders is about 10 to 30% W and that of chelating agents about 0.5 to 6% W--both based on total weight--and in that the acid activator content is such that a pH of the composition between 1 and 6 results.
 8. Rust-inhibiting primer composition according to patent claim 7, characterized in that the resins or binders contain copolymers, for example styrene-butadiene, vinyltoluene/acrylate, polyvinyl acetate or polyvinyl alcohol and/or polystyrene butadiene, that the chelating agents are tannins and/or gallic acid, the actions of which are reinforced with salicylic acid, benzoic acid, resorcylic acid, resorcinol, hydroquinone and/or pyrogallol, and that the acid activators are volatile organic acids.
 9. Process for the preparation of rust-inhibiting primer compositions according to patent claims 1 to 3, characterized in that an oily-organic phase and, separately, an aqueous phase are formed according to the nature of the components, and that during the emulsification of both phases salicic acid gel is added.
 10. Application of the rust-inhibiting primer composition according to patent claims 1 to 3 for priming dry iron and steel surfaces by means of various application methods, whereby a priming coat is obtained which can be coated with the usual finishing emulsion paints.
 11. Process for the preparation of rust-inhibiting primer compositions according to claim 2, characterized in that an oily-organic phase and, separately, an aqueous phase are formed according to the nature of the components, and that during the emulsification of both phases salicic acid gel is added.
 12. Process for the preparation of rust-inhibiting primer compositions according to claim 3, characterized in that an oily-organic phase and, separately, an aqueous phase are formed according to the nature of the components, and that during the emulsification of both phases salicic acid gel is added.
 13. Application of the rust-inhibiting primer composition according to claim 2 for priming dry iron and steel surfaces by means of various application methods, whereby a priming coat is obtained which can be coated with the usual finishing emulsion paints.
 14. Application of the rust-inhibiting primer composition according to claim 3 for priming dry iron and steel surfaces by means of various application methods, whereby a priming coat is obtained which can be coated with the usual finishing emulsion paints. 